Field of the Invention
This invention relates to aqueous polymeric dispersions comprised of graft copolymers of amylopectin starch and vinyl monomers. These compositions have high solids contents (25% by weight or greater) and are stable (show no excessive increase in viscosity and remain homogeneous) over extended periods of time. This invention also relates to processes for the production of the compositions.
Initiators for Graft Polymerization PA0 Starches and Monomers PA0 Graft Copolymer Compositions PA0 Preparation of the Starch Derivatives PA0 Degree of Substitution PA0 Thinning of the Derivatized Starch PA0 Monomers PA0 Polymerization Initiators PA0 Polymerization PA0 Coatings PA0 Sizing Textile Yarns PA0 Activity of Soluble Alpha Amylase PA0 Intrinsic Viscosity PA0 Degree of Substitution
The production of graft copolymers of starch and vinyl monomers initiated by inducing free radicals on a starch is well known. Reviews have been published by J. C. Arthur, Jr. (Advances in Macromolecular Chemistry, Vol. 2, Academic Press, London & New York, pp. 1-87, 1970) and by G. F. Fanta (Block and Graft Copolymers, Vol. 1, John Wiley & Sons, London & New York, pp. 1-45, 1973).
A number of chemical activators are known. U.S. Pat. No. 3,138,564 to Borunsky discloses graft polymerization of 1,3 butadiene and acrylonitrile to starch using ozone and Fe(II). British Pat. No. 869,501 discloses the production of starch graft polymers utilizing polymerization initiators such as hydrogen peroxide, organic peroxides, hydroperoxides and dilute solutions of ceric ions. Yields may be improved by the use of an activator for these initiators such as mild reducing agents, e.g., ferrous ammonium sulfate, sodium formaldehyde sulphoxylate and the like. C. E. Brockway (Am. Chem. Soc. Div. Org. Coatings Plast. Chem., pp. 502-508, 1967) and U.S. Pat. Nos. 3,061,471 to Brockway et al. and 3,061,472 to Brockway disclose the use of hydrogen peroxide to graft polymerize various vinyl monomers onto starch. Additionally, C. E. Brockway (J. Polymer Sci.: Part A, Vol. 2, pp 3721-3731, 1964) discloses use of hydrogen peroxide to graft polymerize methyl methacrylate to starch. For the most part these initiators are nonspecific and induce homopolymerization of single monomers and copolymerization of monomer mixtures as well as the desired graft polymerization of monomer and monomer mixtures to the starch. This produces products which tend to separate on storage.
Such problems can be minimized or avoided by the use of a Cerium(IV) initiator. Although some homopolymerization has been reported using Cerium(IV) by Fanta, et al. (J. Appl. Polymer Sci., Vol. 10, pp. 919-937, 1966) the most important pathway for Cerium(IV) initiation of free radicals as outlined by Fanta (Block and Graft Copolymers, Vol. 1, p. 3, Ed. R. J. Ceresa, John Wiley & Sons, London & New York, 1973) would be expected to give graft copolymers to the exclusion of any homo- or copolymers. Extensive use has been made of this system to graft vinyl monomers to starch.
Brockway et al. in U.S. Pat. No. 3,061,471 and Brockway, U.S. Pat. No. 3,061,472 discuss the graft copolymerization of "thin boiling starch." Brockway uses "starch" in the generic sense to include the various native starches such as corn, potato, waxy maize, tapioca, rice, wheat, etc., the dextrins and the various available modifications and derivatives. In these patents "thin boiling" designates starch products, whether modifications of native starch or derivatives, which when gelatinized produce pastes that are less viscous, cohesive and tacky and tend to gel less than the native starch. Brockway exemplifies these by such starches as the hypochlorite oxidized, the acid-modified, the enzyme converted and the ethers and acetates. The products obtained by polymerization with acrylic acid esters of alkanols are useful as sizes for hydrophobic fibers. U.S. Pat. No. 3,095,391 to Brockway et al. teaches the use of granular unpasted starch, granular hypochlorite-oxidized starch, acid modified granular starch prepared by heating an acidified aqueous suspension of granular starch below the pasting temperature, granular starch reacted with ethylene oxide, and granular starch reacted with vinyl acetate as suitable materials for polymerization with vinyl monomers including vinyl acetate, ethyl acrylate, styrene, methacrylic acid, the butyl esters of acrylic and methacrylic acids, methyl methacrylate, acrylonitrile, acrylamide, 4-vinyl pyridine and diethylaminoethyl methacrylate. The products have utility as adhesives, flocculants and sizes.
The graft copolymerization reactions are usually carried out in aqueous media with the resulting compositions being obtained as aqueous dispersions or latices. Since the valuable and useful portion of such a latex is the graft copolymer portion of the dispersion it is desirable that the compositions be prepared at the highest practicable solids level. Furthermore, if the latices are to have any useful life they must be stable. That is, the dispersions should not separate into two or more phases or undergo any excessive increase in viscosity within the periods required for commercial usage. Such problems when producing polymer compositions from the previously known starches have been noted in U.S. Pat. No. 3,984,361 where gelatinized cationic starches polymerized with a vinyl monomer to form aqueous dispersions are stabilized by sonification and in U.S. Pat. No. 4,029,616 where aqueous dispersions of pullulan polymerized with an ethylenic compound are distinguished from those based on starch by exhibiting stability and not undergoing gelation or "aging."